Series editors' preface - Wood Tools

13
Conserving transparent coatings on
wood
13.1 Introduction to transparent
finishes
Transparent finishes were applied to furniture
to saturate the colour of the wood and offer
some protection for the wood against dirt and
grime. The materials used to make transparent
coatings for wood vary from region to region
and country to country. The finishes applied
to vernacular furniture may differ from that
found in bourgeois or court furniture.
Examples of wooden objects with an intact
original transparent varnish are unusual.
Transparent surfaces on wood have been
viewed in the past primarily in terms of the
function of the object. Aged varnished wood
surfaces were often planed, scraped or sanded
in preparation for refinishing. In some cases
the poor survival of transparent varnishes on
wood can be ascribed to materials included in
their formulation. Colophony, for example,
was often used as an additive to transparent
varnishes for wood. Although colophony
initially reduced the brittleness of the coating,
acidic components have a tendency to crystallize
and contribute to the degradation of the
varnish. Few of the surviving examples of
varnished wood have been analysed. Results
of research that has been undertaken, e.g.
Walch and Koller (1997), have thrown doubt
on much received wisdom.
Whilst the artist or craftsperson may have
intended a coating to be expendable, transparent
coatings on historic and decorated
surfaces are rarely perceived this way by the
collector, curator or conservator. This
inevitably complicates the selection of a
conservation treatment. All natural resins
oxidize and yellow with time. In contrast to
606
easel paintings conservation, where aged and
yellowed varnish is considered unsightly and
usually removed, much of the patination that
is so valued on historic furniture is often
contained within an aged transparent finish.
The deterioration of coatings on wood is
inevitable but they are an important aspect of
the object and may be conserved even when
badly damaged. Too often the only options
considered are those of leaving a coating
untreated or largely removing it. These
extremes are only two of many possibilities
that may be available when conservation
options are reviewed. Removal of an intact but
discoloured original finish will significantly
reduce both the historical and monetary value
of an article of furniture. In general, therefore,
furniture conservators and many restorers
make strenuous efforts to preserve original
aged transparent coatings.
Conservation of transparent surfaces may
draw on traditional materials and techniques
for finishing furniture. To some extent traditional
finishing remains within a craft tradition
with the result that authors and practitioners
vary in their varnish formulations and nuances
of technique. The conservator should apply
both an open mind and a critical approach to
traditional finishing techniques – there is much
to be learned but much also that is not appropriate
to ethical conservation practice.
In the past, the application of protective and
decorative coatings to furniture was the
province of both cabinetmakers and specialist
finishers. Cabinetmakers often opted for
finishes that were easy to apply and imparted
a degree of protection. Historically this may
have meant the use of wax, oil, oil–resin or
resin varnishes whilst modern cabinetmakers